Geology Reports⌕ Search

Geology topics

D. M. Schiffer

Publications and source records attributed to D. M. Schiffer.

5 recordsLinked to original sources
USGS1996

Geohydrology and potential for upward movement of saline water in the Cocoa well field, East Orange County, Florida

The Floridan aquifer system, an approximately 2,000-foot thick sequence of Eocene-age limestone and dolomite, is the main source of water supply in central Florida. Hydraulic conductivity is different in strata of different lithology and is the basis for separating the aquifer system into the Upper Floridan aquifer, a middle semi-confining unit, and the Lower Floridan aquifer. The coastal city of Cocoa withdraws about 26 million gallons of water per day from the Upper Floridan aquifer from a well field in east Orange County, about 25 miles inland. About 60 million gallons per day are withdrawn from the Upper Floridan aquifer and 56 million gallons per day from the Lower Floridan aquifer in the Orlando area, about 15 miles west of the Cocoa well field. Wells drilled in the Cocoa well field from 1955-61 yielded water with chloride concentrations ranging from 25-55 milligrams per liter. Soon after the wells were put in service, chloride concentrations increased; therefore, new wells were drilled further inland. Chloride concentrations in water from many of the new wells also have increased. Possible sources of saline water are lateral movement of relict seawater in the Upper Floridan aquifer from the east, regional upconing of saline water from the Lower Floridan aquifer or underlying older rocks, or localized upward movement of saline water through fractures. Several test wells were drilled to provide information about chloride concentration changes with depth and to monitor changes with time, including a multi-zone well drilled in 1965 (well C) and two wells drilled in the 1990's (wells R and S). Chloride concentrations have increased in the zone pumped by the supply wells (the upper 500 feet of the aquifer) and in the 1,351 to 1,357-foot deep zone of well C, but not in the two intervening zones. This indicates that the source of saline water is located laterally, rather than vertically, from the pumped zone in the area of well C. The potential for upward movement of saline water depends on the direction of the vertical hydraulic gradient and on the vertical hydraulic conductivity of the aquifer. A series of aquifer tests was run in 1993-94 and existing water-level and water-quality data were analyzed to evaluate the potential for upward movement of saline water in the well field. The transmissivity of the upper 500 feet of the aquifer is about 100,000 feet squared per day (the horizontal hydraulic conductivity is about 200 feet per day) and the storage coefficient is about 2x10-4. Horizontal hydraulic conductivities determined from slug tests of the three deepest zones of well C ranged from 20-50 feet per day. Vertical hydraulic conductivities probably do not exceed 0.05 feet per day. The vertical hydraulic gradient is determined by comparing water levels in the various zones, but because of density differences, unadjusted water levels in the deepest zone investigated cannot be directly compared to water levels in the overlying freshwater zones. The difference between environmental-water heads (adjusted for density differences) in the saline-water zone of well C and the overlying freshwater zone were calculated from measured water levels for the period 1966 to 1994. During most of this time period, the gradient was downward, indicating that saline water did not move upward. Upconing of saline water probably is not taking place in the center and western part of the well field, based on the low vertical hydraulic conductivity values estimated for the middle semi-confining unit, the generally downward vertical hydraulic gradient, and the constant chloride concentrations in the intermediate zones of well C. However, there is no information about the extent of the zone of low vertical hydraulic conductivity or about the direction of the vertical hydraulic gradient in the eastern part of the well field. Thus, increased chloride concentrations in supply wells in the eastern part of the well field could be caused either by lateral movement of saline water from the east, or by upward movement from the Lower Floridan aquifer if the low conductivity zone is thin or breached by fractures, or by a combination of both lateral and vertical movement.

Florida↗
USGS1996

Hydrology of central Florida lakes, a primer

Lakes are among the most valued natural resources of central Florida. The landscape of central Florida is riddled with lakes—when viewed from the air it almost seems there is more water than land. Florida has more naturally formed lakes than other southeastern States, where many lakes are manmade, created by building darns across streams. The abundance of lakes on the Florida peninsula is a result of the geology and geologic history of the State. An estimated 7,800 lakes in Florida are greater than 1 acre in surface area. Of these, 35 percent are located in just four counties (fig. 1): Lake, Orange, Osceola, and Polk (Hughes, 1974b). Lakes add to the aesthetic and commercial value of the area and are used by many residents and visitors for fishing, boating, swimming, and other types of outdoor recreation. Lakes also are used for other purposes, such as irrigation, flood control, water supply, and navigation.

Florida↗
USGS1994

Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, May 1994

This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for May 1994. The map is based on water-level measurements made at approximately 1,000 wells and several springs. Data on the map were contoured using 5-foot contour intervals in most areas. The potentiometric surface of this karstic aquifer generally reflects land surface topography. Potentiometric surface highs often correspond to topographic highs, which are areas of surficial recharge to the Upper Floridan aquifer. Springs within topographic lows along with areas of more diffuse upward leakage are natural zones of discharge. Municipal, agricultural, and industrial withdrawals have lowered the potentiometric surface in some areas. The potentiometric surface ranged from 125 feet above sea level in Polk County to 32 feet below sea level in Nassau County. Water levels in May 1994 generally were 0 to 3 feet lower than those measured in May 1993. Water levels in May 1994 in northeast Florida generally were 0 to 3 feet higher than in September 1993, except in the lower St. Johns River basin, where water levels were 0 to 4 feet lower than in September 1993. In the rest of the mapped area, water levels in May 1994 generally were 0 to 4 feet lower than those measured in September 1993.

Open-File Report↗
USGS1989

Effects of three highway-runoff detention methods on water quality of the surficial aquifer system in central Florida

Water quality of the surficial aquifer system was evaluated at one exfiltration pipe, two ponds (detention and retention), and two swales in central Florida, representing three runoff detention methods, to detect any effects from infiltrating highway runoff. Concentrations of major ions, metals, and nutrients were measured in ground water and bottom sediments from 1984 through 1986. At each study area, constituent concentrations in ground water near the structure were compared to concentrations in ground water from an upgradient control site. Ground-water quality data also were pooled by detention method and statistically compared to detect any significant differences between methods. Analysis of variance of the rank-converted water-quality data at the exfiltration pipe indicated that mean concentrations of 14 of 26 water-quality variables are significantly different among sampling locations (the pipe, unsaturated zone, saturated zone, and the control well). Most of these differences are between the unsaturated zone and the other locations. Only phosphorus is significantly higher in ground water near the pipe than in ground water at the control well. Analysis of variance of rank-converted water-quality data at the retention pond indicated significant differences in 14 of 25 water-quality variables among sampling locations (surficial aquifer system, intermediate aquifer, pond and the control well), but mean concentrations in ground water below the pond were never significantly higher than in ground water from the control well. Analysis of variance results at other study areas indicated few significant differences in water quality among sampling locations. Values of water-quality variables measured in ground water at all study areas generally were within drinking water standards. The few exceptions included pH (frequently lower than the limit of 6.5 at one pond and both swales), and iron, which frequently exceeded 300 micrograms per liter in ground water at one swale and the detention pond. Large concentrations of polyaromatic hydrocarbons were measured in sediments at the retention pond but qualitative analysis of organic compounds in ground water from three wells indicated concentrations of only 1 to 5 micrograms per liter at one site, and below detection level (1 microgram per liter) at the other two sites. This may be an indication of immobilization of organic compounds in sediments. Significant differences for most variables were indicated among ground-water quality data pooled by detention method. Nitrate nitrogen and phosphorus concentrations were highest in ground water near swales and the exfiltration pipe, and Kjeldahl nitrogen was highest near ponds. Chromium, copper, and lead concentrations in ground water were frequently below detection levels at all study areas, and no significant differences among detention methods were detected for any metal concentration with the exception of iron. High iron concentrations in ground water near the detention pond and one swale most likely were naturally occurring and unrelated to highway runoff. Results of the study indicate that natural processes occurring in soils attenuate inorganic constituents in runoff prior to reaching the receiving ground water. However, organic compounds detected in sediments at the retention pond indicate a potential problem that may eventually affect the quality of the receiving ground water.

Florida↗